This invention concerns a device for mixing particulate material and liquid, for instance for mixing water and absorbent material which is reactive with gaseous pollutants in flue gases and which, during cleaning of the flue gases, is to be introduced into these gases in moistened state in order to convert the gaseous pollutants to separable dust, said device comprising a container, an inlet for the introduction of particulate material into the container, a spraying means for spraying liquid over the particulate material in the container, an agitator arranged in the container, and an outlet for discharging material mixed with liquid from the container.
When gaseous pollutants, such as sulphur dioxide, are to be separated from flue gases, the gases are conducted through a contact reactor in which particulate absorbent material reactive with the gaseous pollutants is, in moistened state, introduced into the flue gases in order to convert the gaseous pollutants to separable dust. The flue gases are then conducted through a dust separator, in which dust is separated from the flue gases and from which the thus-cleaned flue gases are drawn off. Part of the dust separated in the dust separator is conducted to a mixer, where it is mixed and moistened with water, whereupon it is recycled as absorbent material by being introduced into the flue gases along with an addition of fresh absorbent. As fresh absorbent, use is generally made of slaked lime (calcium hydroxide).
Devices of the type mentioned by way of introduction are used as mixers in order to perform the above mixing operation involving absorbent material and water. In these prior-art devices, the agitator consists of one or more shafts, on which are mounted agitating means in the form of helical flanges, blades, paddles or the like. However, these prior-art devices are not always capable of producing a homogeneous mixture in which the water is evenly distributed in the particulate material. As a result, moist lumps of material may form, especially when the particulate material contains a large proportion of hydrophobic particles, as is the case with fly ash.
In order that the flue gases should be efficiently cleaned, it is, of course, essential that the absorbent material is supplied to the flue gases in the form of a homogeneous mixture in which the moisture is evenly distributed.
A special object of this invention is, therefore, to provide a device which is especially adapted to be used for mixing absorbent material and water in the flue-gas-cleaning method described above and which then results in a homogeneous mixture.
A more general object of the invention is to provide a device which not only results in a homogeneous mixture of particulate material and liquid, but which also has a lower energy consumption than equivalent prior-art devices.
According to the invention, these objects are achieved by a device wherein there is provided a fluidization means adapted to fluidize the particulate material in the container during the mixing operation.
In a preferred embodiment, the container has an upper bottom and a lower bottom, which between them define a chamber and of which the upper bottom is air-permeable, and there is provided an air-supply means adapted to supply air to the chamber with a view to fluidising the particulate material in the container.
Preferably, the agitator consists of at least one rotary shaft which extends along the container and on which a plurality of discs, through the centers of which extends the shaft, are mounted in inclined state at an axial distance from one another. Conveniently, these discs have an elliptic shape and are, about their minor axes, so inclined in relation to the shaft as to have a circular axial projection. In a preferred embodiment, the discs are inclined at an angle of 45.degree.-80.degree., preferably about 60.degree..